The Voice over Internet Protocol (VoIP) is a technique where voice information is packetized and transmitted over a network. VoIP uses signaling to establish, modify, and terminate multimedia events. For example, the Session to Initiation Protocol (SIP) and H.323 represent two methods whereby signaling may be provided.
SIP is an application-layer call control protocol for VoIP and other media applications. The SIP may use redirect and proxy servers. Redirect servers may be used to receive a request from a caller; determine an appropriate destination for the request; and inform the caller of the destination.
Proxy servers may be used to receive a request from a caller and forward the request to the appropriate destination. Proxy servers may be stateless and stateful, and may stay in the call path for the duration of the session, or may allow the source and destination to communicate directly, after an initial proxied message.
In carrier class networks, arrays of SIP proxy servers may be used for increased call capacity and redundancy. However, load balancing preferably occurs between servers so that no one server is significantly loaded than other servers.